In the past, there has been extensive description in the patent and other technical literature of electrophoretic migration imaging processes. For example, a description of such processes may be found in U.S. Pat. Nos. 2,758,939 by Sugarman issued Aug. 14, 1956; 2,940,847, 3,100,426, 3,140,175 and 3,143,508, all by Kaprelian; 3,384,565, 3,384,488 and 3,615,558, all by Tulagin et al; 3,384,566 by Clark; and 3,383,993 by Yeh. In addition to the foregoing patent literature directed to conventional photoelectrophoretic migration imaging processes, another type of electrophoretic migration imaging process which advantageously provides for image reversal is described in Groner, U.S. Pat. No. 3,976,485 issued Aug. 24, 1976.
In general, each of the foregoing electrophoretic migration imaging processes typically employs a layer of electrically photosensitive particles, positioned between two spaced electrodes, one of which may be transparent. To achieve image formation in these processes, the electrically photosensitive particles positioned between the two spaced electrodes, as described above, are subjected to the influence of an electric field and exposed to activating radiation. The electrically photosensitive particles migrate electrophoretically and deposit imagewise on the surface of one or the other of the spaced electrodes. Thus, an image pattern is formed on the surface of these electrodes. Typically, a negative image is formed on one electrode, and a positive image is formed on the opposite electrode.
An essential component of any electrophoretic migration imaging process is the electrically photosensitive particles. To obtain an easy-to-read, visible image it is important that these electrically photosensitive particles be colored, as well as electrically photosensitive. Research efforts to find particles which possess both useful levels of electrical photosensitivity and which exhibit good colorant properties continue.
The art discloses the use of electrically photosensitive particles comprising a polymer and a pigment for use in migration imaging processes. Many of the polymers disclosed for such use, however, have a deleterious effect on the electrically photosensitive particles in that the polymers insulate the particle from the electrodes thereby inhibiting development. For example, British Pat. Nos. 1,242,262 and 1,440,553 disclose the use of polymeric photoconductors in such particles. However, this art does not teach that composite particles which include a polymeric photoconductor have any special utility in improving the results of migration imaging processes. Indeed, only a few photoconductive polymers such as polyvinylcarbazole, are disclosed in the art.